The principal orientation of this long-term project is the determination of the anatomical sites at which and the neurophysiologic mechanisms by which analgesic agents act to suppress the sensation of pain. Among the drugs employed in these studies are morphine, chlorpromazine, pentobarbital and methotrimeprazine. Individual central nervous system neurons will be isolated and examined for their responsiveness to noxious as well as somatic, non-noxious stimuli. The effects of the aforementioned drugs on those units and their responsiveness will be examined.